PROJECT SUMMARY/ABSTRACT Background: The world is facing an enormous and growing threat from the emergence of bacterial `superbugs'. If bacteria continue developing resistance to multiple antibiotics at the present rate and at the same time the antibiotic pipeline continues to dry up, there could be catastrophic costs to healthcare and society globally. Numerous hospitals worldwide have experienced outbreaks of infections caused by multidrug-resistant (MDR) Acinetobacter baumannii, Pseudomonas aeruginosa and Klebsiella pneumoniae. All of these pathogens are on the Infectious Diseases Society of America (IDSA) `hit list' of the six top-priority dangerous bacteria that require urgent attention to discover new antibiotics. The treatment of central nervous system (CNS) infections due to MDR Gram-negative bacteria is problematic and is associated with high mortality rates. Polymyxin B and colistin are the last-line therapy against these very problematic MDR Gram-negative pathogens. The clinical utility of intravenous polymyxins for CNS infections is hindered by their nephrotoxicity and limited penetration into the CNS. In the battle against rapidly emerging resistance we can no longer rely on the discovery of new antibiotics. We must optimise the use of existing antibiotics through the application of systems pharmacology combined with pharmacokinetics /pharmacodynamics (PK/PD) to increase efficacy while minimising toxicity and resistance. Delivery of polymyxin antibiotics directly into the CNS shows very promising potential for the treatment of infections caused by bacterial `superbugs'. Unfortunately, current dosing recommendations of intrathecal and intraventricular (ITH/IVT) polymyxins are entirely empirical due to the lack of PK/PD data and, importantly, there are no data on potential neurotoxicity. Research Design: This multi-disciplinary project aims to elucidate the mechanism of disposition and potential toxicity of ITH/IVT polymyxins using cutting-edge imaging and systems pharmacology, and to optimise the therapy in a rat CNS infection model. The Specific Aims are to: (1) investigate the CSF pharmacokinetics of ITH/IVT polymyxins in a rat CNS infection model with A. baumannii, P.aeruginosa and K. pneumoniae; (2) elucidate the disposition of polymyxins in neuronal cells and CNS tissue using cutting-edge imaging techniques; (3) investigate the potential neurotoxicity of ITH/IVT polymyxins using systems pharmacology; and (4) optimise dosage regimens of ITH/IVT polymyxins for the treatment of Gram-negative CNS infections using a rat CNS model and mechanism-based PK/PD modelling. Significance: Our innovative proposal will provide the first-ever PK/PD and toxicity data to support safer and more efficacious ITH/IVT therapy of polymyxins for life-threatening CNS infections due to Gram-negative `superbugs'. It will have a significant potential in improving clinical practice worldwide.